It is a standard practice to provide the heater of an automotive vehicle with means for mixing relatively fresh outside air with the air being heated, to ventilate the passenger compartment of the vehicle while at the same time tempering the heating effect. The ratio of the modified/fresh-air mixture is normally controlled by a flap in the heating apparatus. Such a system is also frequently employed in the summer when the vehicle is air-conditioned to replace the recirculated air in the passenger compartment so as to prevent the air in the passenger compartment from becoming too stale.
It is also known, as for example from German Pat. publications Nos. 1,753,300 and 2,141,809, to provide a pair of outlets for such a heating/ventilating apparatus, one outlet opening at the driver side of the vehicle and the other at the passenger side. Such an arrangement is provided because normally the driver is considerably more active than the passenger, so the driver wishes less heat in the water and more cooling in the summer. The systems described in these publications therefore allow individual control to at least a limited extent of the heating for the two sides of the vehicle passenger compartment.
The one system described in the publications above simply allows heated air to be diverted to one side or the other. It is not possible with this system to vary the temperature from one side to the other, merely to completely eliminate heating from one side if desired. The reduction, for example, of the heating on the driver side has the effect of simultaneously cutting back the supply of fresh air to the driver, and vice versa.
In other more complex systems it is possible to achieve an individual temperature control for each side by providing relatively complex dual heaters, so that the overall installation cost is elevated.